“Permanent” hair color products and lighteners typically work by lightening the hair's natural pigment (melanin), and then replacing the melanin with the desired shade of color. The color is often achieved through oxidizable dye intermediates (typically para- and ortho-aromatic diamines, which are readily oxidized and are necessary for the dark shades and depth of color) and preformed dyes or tints. A developer (oxidizing agent, usually peroxide based) is used to strip away natural pigment and to activate the dyes and couplers. An alkalizing agent (usually an ammonia solution) also reacts with the dye intermediates to help impart the desired color. To prevent premature reaction, the developer is typically isolated in a separate bottle from the alkalizing agent.
Both peroxides and ammonia compounds are known to damage hair, and their reaction swells the hair cuticle, permitting the color to enter the cortex, but also understandably rendering the hair more fragile. Current cationic conditioners are incompatible with hair dye formulations. As can be appreciated, it is a major challenge in the art to create as little damage to the hair as possible while coloring it. At the same time, it is incredibly important not to affect the complex color reactions necessary to achieve the exact desired color.